Throughout Star Wars, the Empire has always shown strength through its large milliary power. Easily one of the most iconic of its vehicles were the Star Destroyers, which were frequently used to blockade and bombard planets. Yet even they paled in comparison to the Super Star Destroyer seen in Star Wars: Return of the Jedi, which was larger than any other Imperial ship. However, the massive craft was blown up during the Battle of Endor, which raises questions as to how it was destroyed so easily by a single A-Wing.
The Super Star Destroyer, appropriately named the Executor, stood as a command ship for all other Star Destroyers. As described in the Star Wars encyclopedia, the Executor measured a staggering 19,000 meters in length and was equipped with top-of-the-line defenses. Not only that, it held a crew of over 300,000 people and stored over 1000 ships. So, the relatively small Rebel Alliance managed to score a huge victory when it brought the vessel down.
During the Rebels' desperate attempt to survive Endor, they scrambled among the Star Destroyers to hide from the Death Star II. Amid the chaos, a small A-Wing fighter was struck and headed straight for the Executor's bridge. Admiral Piett yelled to intensify the forward batteries, but it was already too late, and the small craft plummeted through the bridge with ease. With the small fire left from the crash, the Executor then dove straight into the side of the Death Star II and was completely blown to pieces.
Given the size and power of the Super Star Destroyer, its destruction can seem a little too easy. However, many factors led up to its demise. In the novel Star Wars: Lost Stars, it's mentioned that the Executor's engines had been weakened from previous Rebel skirmishes. And so, the ship was already at a disadvantage during Return of the Jedi, and the smoking engine can even be spotted during the battle.
As the Rebels scrambled for safety, Admiral Ackbar yelled out, "Concentrate fire all on that Super Star Destroyer!" From this endless barrage of attacks, the ship's deflector shields were blown up, meaning the bridge was left with minimal protection. While it could hold out against lasers, the force of a craft diving head-first into the Executor was too much, and everyone on the bridge met their end.
This then set off a string of bad luck as the Destroyer began to uncontrollably turn due to its damaged engine. With the ship sitting too close to the gigantic Death Star II, it's likely the space station's gravitational pull brought the Executor in its direction. And with no crew left alive to steer away, there was nothing left but the inevitable crash and explosion.
And so, as seen many times, the Empire clearly underestimated the Rebels and died due to its incompetence. With a mixture of an already damaged engine, poor commands from Piett, and the sacrifice of an A-Wing pilot, the largest Imperial craft was finally brought down. And it perfectly sums up the Rebels of Star Wars, as through hope, persistence and sacrifice, they were able to take down an entire Empire, all while vastly outnumbered.